Johns Hopkins University and its partners in Thailand and India are pleased to propose the JHU Southern Asia Clinical Trials Unit, David D. Celentano, Principal Investigator. This CTU focuses on recruiting injecting drug users (IDU) and high risk Asian populations affected by the HIV/AIDS epidemic, into phase IIb and III clinical trials investigating novel strategies to prevent HIV infection. We will address two of the high priority clinical research areas identified by DAIDS in its RFA-AI-05-002: Prevention of HIV Infection and Microbicides. For prevention of HIV infection we will affiliate with the proposed HIV Prevention Trials Network. The JHU Southern Asia CTU consists of an administrative component at Johns Hopkins and clinical research sites (CRS) in northern Thailand and southern India. In northern Thailand we are proposing a cluster of research sites led by the Research Institute for Health Sciences (RIHES) at Chiang Mai University (CMU) (Thira Sirisanthana, site leader). In southern India we propose a research site at the YR Gaitonde Center for Substance Abuse-related Research (YRG CSAR), Chennai (Suniti Solomon, site leader). We have longstanding research collaborations with both these units, and have been collaborators on past HPTN studies. Three HPTN studies are under way at the Chiang Mai site and will continue into the period this RFA. HPTN 037, a Phase III behavioral study of the efficacy of a social network intervention in preventing HIV infection among IDUs, began in Chiang Mai in March 2004; the site has a recruitment target of 1,740 volunteers; we propose expanding enrollment to the Chennai site. HPTN 043, a Phase III study of the effectiveness of community based voluntary counseling and testing to prevent HIV infection at a community level, is being carried out in 14 communities in northern Thailand. This study is largely supported by NIMH but was developed by the HPTN; the baseline survey began in January 2005, with interventions beginning in September 2005. HPTN 052, a Phase III IND clinical trial, of the efficacy of antiretroviral therapy in reducing sexual transmission of HIV among discordant couples, began in Chiang Mai in June 2005 with a site enrollment target of 243 couples. A fourth HPTN protocol under development, HPTN 058, is expected to begin in Chiang Mai, and expand to Chennai, in the next year. This is a Phase III IND clinical trial of the efficacy of opioid substitution therapy with buprenorphine/naloxone for prevention of HIV infection.